This invention relates to a Coriolis flowmeter and in particular to a single tube Coriolis flowmeter structure for connecting the vibrating elements of the Coriolis flowmeter to the flowmeter case. The invention further relates to a Coriolis flowmeter that can be manufactured, tested, calibrated, and stored prior to the attachment of process connection flanges.
It is a problem to provide a single flow tube Coriolis flowmeter that operates satisfactorily over a wide range of variations in the operating parameters of the flowmeter. These parameters include operating temperature, the density of the material flow as well as the material pressure and flow rate. A change in material density, thermally induced stress in the flow tube, or pressure stress on the flow tube can each result in an unbalanced condition which effects the accuracy of the flowmeter. Changes in these parameters degrade the static and dynamic isolation of the vibratory elements of the flowmeter. The problem is to keep the vibratory elements immune from the effects of changes in operating parameters. The accelerations that result from the change in operating parameters impair flowmeter accuracy by adding to or subtracting from the Coriolis acceleration of the material. The unwanted accelerations cannot be compensated for because they vary with the mounting conditions of the flowmeter. In addition, the mounting conditions often change with time and temperature in unknown ways.
Even though a variation of the material parameters and mounting conditions is to be expected, it is desired that the flowmeter remain operational and produce accurate output information. It is also desired that the structural integrity of the flowmeter elements be maintained as these parameters vary. It is a goal to design a Coriolis flowmeter so that it operates with suitable accuracy and does not destroy itself as the flowmeter elements are subject to varying operating temperatures. Flowmeter designers also desire that the flowmeter calibration will remain constant and flat over a reasonably wide range of material densities.
In order to achieve these design objectives, a Coriolis flowmeter must have a dynamically balanced vibrating structure that operates in a controlled and predictable manner over a range of operating parameter variations. The flowmeter elements external to the vibrating system should not vibrate or communicate vibration to the vibratory system. A Coriolis flowmeter often comprises a single straight flow tube surrounded by a balance bar and brace bars coupling the balance bar ends to the flow tube. In operation, vibration nodes (regions of no vibration) occur between the flow tube and the balance bar. The nodes define the length of the flow tube that is subject to Coriolis force. The vibration nodes of the flow tube and the surrounding balance bar should remain in the brace bars over the range of parameters for which the flowmeter is designed. Since the balance bar, brace bar, and flow tube comprise a dynamically balanced system, the vibrating mass times the vibration velocity of the balance bar should equal the vibrating mass times the vibration velocity of the flow tube. As long as these conditions are met, and no other unbalanced forces or torques are applied to the non-vibratory elements of the flowmeter, the vibration nodes remain in the brace bars and the other flow meter elements remain free from vibration. However, prior art attempts have all fallen short of meeting these conditions.
A prior art attempt to minimize node movement and the communication of vibration from the case to the vibratory system is shown in the U.S. Pat. No. 5,473,949 to Cage. This patent discloses a straight tube Coriolis flowmeter having a flow tube and a surrounding balance bar coupled by brace bars. The design is unique in that each brace bar also comprises a portion of each case end of the flowmeter. This geometry uses the mass of the case to keep the vibration nodes near the brace bar. For instance, a high density material in the flow tube causes the vibration nodes to move very slightly into the active portion of the flow tube with the result that the brace bars and case ends (and case) move in phase with the balance bar. Momentum is conserved since the mass times velocity of the case plus the mass times the velocity of the balance bar equals the mass times velocity of the flow tube. A low density material causes the node to move slightly into the balance bar with the result that the case moves in phase with the flow tube and momentum is once again conserved. The problem with the Cage design is that momentum is conserved by the case moving with the light member. The vibration is of small amplitude because the case is massive, but it is still large enough that different mounting conditions can effect the accuracy of the meter.
Another example of a prior art flowmeter that attempts to minimize unwanted accelerations is shown in U.S. Pat. No. 5,365,794 to Krohne. This patent discloses a flow tube surrounded by a concentric balance bar and distinct brace bars that couple the balance bar ends to the flow tube. In this design the balance bar ends are not connected to the case as in the Cage design. Furthermore, the inactive portion of the flow tube, external to the brace bar regions, is not connected to any of the support structure except by the tube ends that are connected to the flange faces. This structure operates satisfactorily as long the ratio of the vibration amplitude of the flow tube divided by the vibration amplitude of the balance bar does not vary from its design point. At the design point, the torque applied to the brace bars by the flow tubes is equal and opposite to the torque applied to the brace bars by the balance bar. The result is that the inactive portions of the flow tube are indeed inactive and remain on the axis of the meter. The problem arises when the material density changes. A high density material causes the vibration amplitude ratio to change. To conserve momentum the vibration amplitude of the heavy flow tube decreases while the vibration amplitude of the balance bar increases. The change in amplitude ratio causes the torques at the brace bar to become mismatched. The higher amplitude balance bar applies more torque to the junction than the lower amplitude flow tube. The inactive portion of the flow tube makes up the torque difference and bends as a result. Unfortunately, the translation increases the amplitude of the heavy flow tube and makes the balance worse. Ultimately, the flow tube (containing the high density material) ends up vibrating in phase with the case and the vibration nodes move far from their balanced locations and the meter accuracy suffers.
EPO patent 0,759,542 by Oval (FIGS. 8A and 8B of EPO patent 0,759,542) provides a Coriolis flowmeter having a straight flow tube surrounded by a concentric balance bar whose ends are coupled by case connect links to the inner wall of a case. The flow tube ends are coupled to end flanges. This structure provides dual connection points at each end of the flowmeter between the balance bar/flow tube and the case structure including the end flanges. The case connect link design uses the mass of the case to help reduce the movement of the end nodes (as in the Cage design). However, large changes in the amplitude ratio cause torque unbalance at the brace bars (like the Krohne design) and bending in the inactive regions of the flow tube. While the vibration is less than with the other prior art, it is still sufficient to degrade the meter performance.
It can therefore be seen from the above that it is a problem of prior art to provide a Coriolis flowmeter structure for which a shift of the material density does not degrade the static and dynamic isolation of the flowmeter""s vibratory system and the corresponding reduction in the accuracy of the meter.
It is also a problem in the manufacture, calibration and testing of a Coriolis flowmeter to minimize the number of Coriolis flowmeters of a given model that must be maintained in inventory. The reason for this is that there are more than twenty different types of end flanges that may be coupled to each size of flowmeter. There are perhaps eight different sizes of flowmeter resulting in 120 different meters that need to be stocked in order to have rapid response to sales orders. At a cost of several thousand dollars each, the amount of money tied up in inventory can be significant. It is desired that flowmeters be of such a design that they can be balanced, tested, and calibrated before the flanges are attached. This would enable the stocking of far fewer finished meters without flanges. The desired flanges would be welded on with the receipt of each order. Of the prior art meters, only the Cage design would be functional without flanges and it has balance problems. The other two prior art designs require that the tube end be welded to the flange in order to provide the dynamics of the finished meter.
The above problems are solved and an advance in the art is achieved by the present invention. In accordance with the present invention, three separate connection points are provided at each end of the flowmeter between the vibrating structure and the flowmeter case including the end flanges. A first such connection point is in the end flange where the flow tube end is joined to the end flange. A second connection point is provided by case connect links which couple the balance bar ends to the inner wall of the case.
The third connecting point in each end of the flowmeter is provided by a circular element termed a cone connect. This third connection point is provided by bonding (usually brazing) the flow tube to the cone connect element at the flow tube location where it extends through an opening in the case end and projects axially outward towards the flow tube end. This cone connect connection is, like the other two connections, of limited length in the direction of the tube axis. There is a length of unsupported flow tube between the flange connection and the cone connect and another length of unsupported flow tube between the cone connect and the case connect links. Since these unsupported portions of the flow tube are not coupled to any other structure, a void surrounds these portions of the flow tube. The outermost void (in the neck of the flange) allows the welding of a flange to the case end at this location without overheating or stressing the flow tube. Also, the amount of heat required to effect a weld at these two locations is far less than would be required if the entirety of this portion of the flow tube was thermally coupled to the entire structure between the end flange and the case end.
The provision of three points of coupling at each end of the flow tube to the supporting structure of the flowmeter minimizes the communication of vibrations to the vibratory structure of the flowmeter that are generated by extreme conditions of parameters such as material density. It does this by the use of the case connect links to enable vibration amplitude ratio balancing and it uses the cone connect element to keep unbalanced torque away from the vibratory structure of the flowmeter. The reduced communication of vibrations to the vibratory structure of the flowmeter increases the accuracy and reduces the effect that different mounting conditions have on the flowmeter.
It is a further feature that the flowmeter of the present invention is manufactured, tested, and calibrated prior to the time that the end flange is actually attached. At this stage of completion, the internal elements of the flowmeter are fully operational and are sealed or isolated by the cone connect element. The end portions of the flow tube extend axially outward from each of the case ends and their cone connect elements. Because the case is sealed and the flow tubes are rigidly affixed to the case ends, the tube ends may be temporarily coupled to a source of material flow at this time. The flowmeter may then be balanced and calibrated. The flowmeter may be indefinitely stored in this state until an order is received from a customer. Then, the needs of the customer and the details of the end flanges required by the customer are made known and the appropriate end flanges may be coupled to the flow tube projections and the case ends by suitable welding operations.
The calibration and testing and subsequent temporary storage of the flowmeter prior to it being connected to end flanges is advantageous in that it minimizes the inventory that otherwise would have to be maintained by a supplier. If finished flowmeters were required to be stored with over twenty known types of flanges, the inventory would have to be enormous.
An alternative embodiment of the invention provides a case connect link that is not directly connected at its ends between the balance bar and the inner wall of the case. Instead, the case connect link has a bend in its central portion and has its outer end connected to a flat surface of the cone connect element. In this second embodiment, the cone connect link is circular as in the first embodiment but has a larger diameter with the outer circumference of this circular cone connect element engaging the inner circular surface of the flowmeter case end. By this means, the case connect link has sufficient rigidity to prevent relative motion between the balance bar ends and the inner wall of the case. At that the same time, due to the bend in the case connect link, the case connect link is able to flex and accommodate changes in the diameter of the balance bar due to thermal changes. The circular cone connect element functions as before described in that it has an opening in its center portion through which the flow tube extends. It differs in that the large outer diameter of the cone connect allows relative axial movement between its outer and inner connection points. This compliance can lower the thermal stress in the flow tube. The cone connect element of this embodiment, like the previous embodiment, also has sufficient rigidity in the radial direction to terminate the dynamic portion of the flow tube and allow balancing and calibration prior to flange welding. It also seals the case interior from the environment
It can therefore be seen from the above that the present invention is advantageous in that it provides a flowmeter structure that maintains the dynamic isolation of the vibratory system of the flowmeter. It further permits the flowmeter to be tested, calibrated, and stored in a state in which it is devoid of a flange; the flange being installed only when the specific model of flange required by the customer is known.
An aspect of the invention includes:
A Coriolis flowmeter having a flow tube and a balance bar that are adapted, when in use, to be vibrated in a driven plane in phase opposition to generate a Coriolis response in said vibrating flow tube representing information pertaining to material flowing through said vibrating flow tube,
a case enclosing said flow tube and said balance bar with said balance bar being substantially parallel to and surrounding said flow tube;
a first and a second end of said case;
an opening in each of said case ends for receiving end portions of said flow tube that project beyond said case ends;
said opening in said case ends is coaxial with a longitudinal axis of said flow tube;
brace bar means coupling ends of said balance bar to said flow tube;
case connect link means having a first end coupled to said brace bar as well as to said balance bar and having a second end coupled to an inner wall of said case;
said case connect link means is effective to inhibit the movement of said brace bar and said balance bar ends in a direction perpendicular to said longitudinal axis of said flow tube in said driven plane;
a cone connect means having an outer circumference coupled to said case end and having a circular opening coaxial with said flow tube for sealably receiving said flow tube; and
said cone connect means being axially positioned between a terminus of said flow tube and said case connect link means.
Another aspect comprises:
a cylindrical neck of said case end extending axially outward from said case end;
said neck has a center opening coaxial with said flow tube and a cylindrical inner surface that surrounds a portion of said flow tube that projects beyond said case end;
said cylindrical inner surface of said neck has a greater diameter than the diameter of said flow tube; and
a circular cavity in said neck defined by the space between said flow tube and said cylindrical inner surface of said neck.
Another aspect includes an out of plane bend in a planar surface of said case connect links.
Another aspect is that said circular cone connect means has a flat surface having an out of plane bend to permit a change in the effective diameter of said circular cone connect means in response to changes in the diameter of the portion of said case end to which said cone connect means is coupled.
Another aspect is that said coupling of second end of said case connect link means comprises a connection of said second end of case connect link means to said inner wall of said case.
Another aspect is that said second end of said case connect link means is coupled to said wall of said case by an intermediate connection means that is connected to said inner wall of said case.
Another aspect is that said intermediate connection means includes a surface of said cone connect means whose perimeter is connected to a surface of said inner wall of said case.
Another aspect is that a driver that vibrates said flow tube and said balance bar in a drive plane in phase opposition to each other;
said vibrations in said drive plane and said material flow are jointly effective for inducing Coriolis deflections in said flow tube;
pick off means coupled to said flow tube that detect said Coriolis deflections;
said pick off means generate signals representing information pertaining to said material flow in response to said detection of said Coriolis deflections; and
meter electronics that receive said signals from said pick off means and generates output information pertaining to said material flow.
Another aspect is that said flow tube extends at a constant diameter for the length of said case and has said ends portions that project through said opening in said cone connect means at said constant diameter to said terminus of said flow tube.
Another aspect is that said terminus of each said end portion of said flow tube is devoid of attachment to any other structure.
Another aspect includes an end flange coupled to said terminus of each said end portion of said flow tube for enabling said Coriolis flowmeter to be coupled to a pipeline;
a raised element having a circular opening on an axial end of said flange, and
walls of said center opening that sealably engage said flow tube.
Another aspect includes a sealed cavity defined by space between the outer surface of said end portion of said flow tube and said inner cylindrical surface of said neck of said case end and a cylindrical inner surface of a portion of said end flange;
said sealed cavity having an axially outer end comprising opening of said raised element of said end flange sealably engaged with said flow tube;
said sealed cavity having an axially inner end comprising said opening in said cone connect means that is in sealable engagement with said flow tube.
Another aspect includes a sealed cavity defined by space between the outer surface of a portion of said flow tube and an inner cylindrical surface of said neck of said case end and a cylindrical inner surface of a neck of said end flange;
said sealed cavity has an axially outer end comprising said raised element of said end flange that is sealably engaged with said flow tube;
said sealed cavity has an axially inner end comprising said opening in said cone connect means that is sealably engaged with said flow tube.
Another aspect includes an end flange;
a neck of said end flange having a first end comprising said end flange and having second end connected to an axially outer end of said neck of said case end;
a cylindrical opening in said end flange and in said neck of said end flange for receiving said terminus of said end portion of said flow tube;
said cylindrical opening in said neck of said end flange and in a portion of said end flange has a diameter that is substantially greater than the exterior surface of said flow tube to define a void between said exterior surface of said flow tube and said cylindrical inner surface of said neck of said end flange and a cylindrical inner surface of said portion of said end flange; and
a raised element having a center opening in an axially outer portion in said end flange that has an inner diameter for sealably receiving the terminus portion of said flow tube.
Another aspect includes said case includes walls parallel to the longitudinal axis of said flow tube;
said case further includes said case ends which are affixed to ends of said walls and are oriented substantially perpendicular to said cylindrical walls;
the exterior surfaces of said case ends include a circular lip coaxial with said opening in said case ends for defining said cone connect means and for receiving said portion of said flow tube that projects beyond said case ends;
said case ends further including a neck having a cylindrical inner surface of a greater diameter than the exterior surface of said flow tube to define a void comprising the space between said exterior surface of said flow tube and said inner surface of said neck.
Another aspect includes an end flange coupled to said terminus of said flow tube for enabling said Coriolis flowmeter to be coupled to a pipeline.
Another aspect includes cylindrical walls oriented parallel to the longitudinal axis of said flow tube;
said case ends are curved and offset from perpendicular with respect to said cylindrical walls;
an inner surface of a curved portion of said case end includes means that receives the outer extremity of said circular cone connect means;
said flow tube extends the length of said case and has said end portions that extend through a center opening of said cone connect means and through said cavity of said neck of said case end to a flow tube terminus axially beyond said neck.
Another aspect is that said terminus of said flow tube is devoid of attachment to any other structure.
Another aspect is that an end flange coupled to said terminus of said flow tube for enabling said Coriolis flowmeter to be coupled to a pipeline.
Another aspect includes cylindrical walls oriented parallel to the longitudinal axis of said flow tube;
said case ends have a curved portion that is offset from perpendicular with respect to said cylindrical walls;
an inner surface of an axial inner portion of said case end has a diameter equal to the inner diameter of said case for receiving the outer extremity of said circular cone connect means;
said flow tube extends the length of said case and has said end portions that extend through a center opening of said cone connect means and through said cavity of said neck of said case end to a flow tube terminus axially beyond said neck.
Another aspect is that said terminus of each said end portion of said flow tube is devoid of attachment to any other structure.
Another aspect includes an end flange coupled to said terminus of said flow tube for enabling said Coriolis flowmeter to be coupled to a pipeline.
Another aspect is that said Coriolis flowmeter further includes:
an end flange;
a cylindrical opening in said end flange for receiving said terminus of said end portion of said flow tube;
a neck of said end flange having a first end integral with an axially outer portion of said end flange and having an axially inner end connected to an axially outer end of said neck of said case end;
said end flange and said neck of said end flange both have a cylindrical inner surface coaxial with said flow tube;
said cylindrical inner surface opening in said neck of said end flange as well as in an axially inner portion of said end flange has a diameter that is substantially greater than the exterior surface of said flow tube to define a void between said exterior surface of said end portion of said flow tube and said cylindrical inner surface of said neck of said end flange and said axially inner portion of said end flange; and
an axially outer portion of said cylindrical opening in said end flange defines a raised element that has a diameter approximate that of said flow tube diameter for sealably receiving the terminus of said flow tube.
Another aspect is that said case connect link comprises:
a flat elongated member having a bend in a mid portion of said member to define two legs of said member that are angularly oriented with respect to each other;
an outer end of a first one of said legs being connected to an end of said balance bar;
an outer end of a second one of said legs being connected to a surface of said cone connect means to define a series path connecting said end of said balance bar with said inner wall of said case;
said series path comprises said first and second legs of said case connect link and a portion of said cone connect means.
Another aspect includes said two legs are oriented substantially 90 degree with respect to each other;
Another aspect is that said terminus of said flow tube is devoid of attachment to any other structure.
Another aspect includes an end flange coupled to said terminus of said flow tube for enabling said Coriolis flowmeter to be coupled to a pipeline.
Another aspect is that said case connect link comprises:
a flat elongated curvilinear member;
an outer end of a first one of said legs being connected to an end of said balance bar;
an outer end of a second one of said legs being connected to a surface of said cone connect means to define a series path connecting said end of said balance bar with said inner wall of said case;
said series path comprises said case connect link and a portion of said cone connect means.
Another aspect is that said case connect link comprises:
an elongated member having at least one bend;
an inner end of said elongated member is connected to an end of said balance bar;
an outer end of said elongated member is connected to a surface of said cone connect means to define a series path connecting said end of said balance bar with said inner wall of said case;
said series path comprises said case connect link and a portion of said cone connect means.
Another aspect includes a method of forming a Coriolis flowmeter having a flow tube and a balance bar that are adapted, when in use, to be vibrated in a driven plane in phase opposition to generate a Coriolis response in said vibrating flow tube representing information pertaining to material flowing through said vibrating flow tube, said method comprising the steps of:
enclosing said flow tube and said balance bar in a case with said balance bar being substantially parallel to said flow tube;
said case having first and a second ends;
including an opening defining a cone connect in each of said case ends for receiving end portions of said flow tube that project beyond said case ends;
sealably coupling said opening in said cone connect to said flow tube;
coupling ends of said balance bar to said flow tube with brace bar means;
coupling said brace bar and said balance bar to an inner wall of said case with case connect link means;
said case connect link means is effective to inhibit the movement of said brace bar and said balance bar ends in a direction perpendicular to a longitudinal axis of said flow tube in said driven plane;
forming a cylindrical neck on said case end having a center coaxial with said flow tube and extending axially outward from said case end;
said neck surrounds said end portion of said flow tube that projects beyond said case end and has an inner cylindrical surface of a greater diameter than the diameter of said flow tube;
forming a circular cavity in said neck is defined by the space between the outer surface of said end portion of said flow tube and said cylindrical inner surface of said neck;
extending said flow tube at a constant diameter for the length of said case so that said ends portions of said flow tube project through said opening in each case end at said constant diameter to a terminus beyond each said case end; and
said terminus of each end portion of said flow tube is devoid of attachment to any other structure.
Another aspect includes the step of:
affixing an end flange to said terminus of said flow tube to enable said Coriolis flowmeter to be coupled to a pipeline.